Various types of moving walkways have been proposed in the past, including constant speed walkways as well as more sophisticated walkways capable of undergoing acceleration and deceleration. Walkways of the latter type have been disclosed, for example, in U.S. Pat. No. 3,939,959, entitled Accelerating and Decelerating Moving Walkway, and in U.S. Pat. No. 4,276,976 entitled Accelerating and Decelerating Moving Walkway With Minimal Walkway Surface Irregularities. Such walkways include serially connected, overlapping platforms that travel along an elongated, generally horizontal path of travel that includes a pair of oppositely travelling, parallel walkway surfaces positioned adjacent one another. At the opposite ends of the circuit the walkway platforms reverse direction beneath stationary cover plates that form combined entry and exit thresholds.
The platforms of walkways of the type disclosed in the above-referenced U.S. patent are connected together by flexible mechanical linkages whose length is varied to control platform overlap. More specifically, the lengths of the mechanical linkages are controlled by cam followers that are actuated by rail cams located beneath the platforms. In operation, the amount of overlap between adjacent platforms is varied in selected zones of the walkway path of travel to effect deceleration and acceleration of the walkway. For example, as the walkway platforms emerge at a relatively low speed from under an entry threshold they pass through an acceleration zone wherein the amount of overlap between adjacent platforms is decreased so as to draw apart the platforms and accelerate a passenger standing on the walkway. The platforms then pass through a constant speed zone that typically constitutes a major portion of the length of the walkway. In the constant speed zone the overlap between adjacent platforms is reduced to a minimum to transport passengers at the maximum desirable speed. As the platforms approach an exit threshold at the end of the constant speed zone the platforms pass through a deceleration zone wherein the platforms are brought closer together to decrease the amount of overlap between adjacent platforms and thereby decelerate passengers to a speed sufficiently low to step safely off the walkway.
Various types of drive systems have been proposed for driving moving walkways of the type thus far described. For example, the drive system of the walkway disclosed in U.S. Pat. No. 3,939,959 includes a pair of drive belts (or chains). Each drive belt travels in a relatively short loop beneath a portion of a constant speed zone of the walkway. Affixed to each drive belt are collars that engage cooperable lugs, which project downwardly from the walkway platforms. The drive belt, through the collars, engages and drives the immediately overlying platforms, with the remainder of the platforms in the walkway being pulled along the path of travel by the driven platforms.
The major disadvantage of the drive system described above is that power is applied directly at any given moment only to a limited number of platforms, i.e., those travelling directly over the drive mechanisms. Accordingly, the force required to drive the other platforms, particularly those travelling through the change-of-direction regions at the ends of the walkway, must be transmitted through the flexible mechanical linkages connecting serially adjacent platforms. Even though these linkages are simple and efficient devices for transmitting mechanical loads, the large number of mechanical connections in series results in a substantial energy loss, on the order of 90%, and proportionately high reaction loads in the platform-connecting devices.
Further, the direct application of power to only a relatively few platforms in the constant speed zones, together with the large energy loss incurred as the platforms travel through the change-of-direction regions, results in large imbalances in the tensile loads borne by the platform-connecting devices. For example, a large tensile load is borne by the connecting devices between the last platform engaged by a drive mechanism and the immediately succeeding platform, whereas only a minimal tensile load is borne by the connecting device between platforms just leaving the drive mechanisms. These large variations in the tensile drive load require that all of the platforms, their associated connecting mechanisms and the walkway-supporting structures be designed to bear the maximum tensile loads, thereby increasing the total weight, cost, and power requirements of the walkway.
Another problem that occasionally arises in moving walkways, wherein power is applied only to a limited number of platforms, is low-frequency mechanical oscillation. Oscillation can occur in any walkway consisting of serially linked platforms, although it is a particularly troublesome problem when the platforms are not rigidly linked together, for example, because of play in the linkages or due to flexible or nonrigid couplings between platforms. If not damped or otherwise prevented, oscillation can impair the operation of the walkway, particularly if it occurs at a resonant frequency.
Accordingly, it is the general object and purpose of the present invention to provide a new and improved drive system for a moving walkway. In particular, it is the object of the invention to provide a drive mechanism for a moving walkway having a plurality of overlapping platforms connected in series.
More specifically, it is an object of the present invention to provide a drive system for an accelerating and decelerating moving walkway comprising a plurality of overlapping platforms wherein acceleration and deceleration are effected by varying the amount of overlap between adjacent platforms.
It is another object of the present invention to attain the foregoing objects and purposes with a drive system that engages and drives a plurality of walkway platforms along constant speed zones as well as along change-of-direction regions.
It is another object to provide a drive system for a moving walkway that avoids, or at least minimizes, oscillation of the walkway.
It is another and more specific object of the present invention to provide a drive system for an accelerating and decelerating moving walkway generally of the type disclosed in U.S. Pat. No. 3,939,959 and in U.S. Pat. No. 4,276,976, which drive system engages and drives a plurality of platforms travelling through constant speed zones at a first, relatively high speed, and which also simultaneously engages and drives a plurality of platforms travelling through the change-of-direction regions at a second, relatively low speed.